Apparatus and method for alarming decrease in tire air-pressure

ABSTRACT

An apparatus for alarming a decrease in tire air-pressure which alarms the decrease in inner pressure of the tire by using a judged value calculated based on wheel speed information obtained from tires fitted to a four-wheeled vehicle. The apparatus comprises calculating means for calculating the judged value based on the wheel speed information on each of the tires, the calculating means being connected to one of on-vehicle LANs, via which the wheel speed information on each of the tires is transmitted. The calculates means captures the wheel speed information on each of the tires via one of the on-vehicle LANs. The wheel speed information is converted into the digital data, which is then captured into the apparatus for alarming the decrease in tire air-pressure via the on-vehicle LAN, thus remarkably reducing the number of lines laid in the vehicle in comparison with the prior art.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an apparatus and a method foralarming a decrease in tire air-pressure and, more particularly, to anapparatus and a method for alarming a decrease in tire air-pressure, inwhich an installation space can be saved and the cost of manufacturingcan be reduced.

[0002] As a safety device for a four-wheeled vehicle such as a passengercar, there has been conventionally known an apparatus for alarming adecrease in tire air-pressure of a system for detecting a change in tireair-pressure based on variations in wheel speed information. Such anapparatus is configured such that a sine-wave analog signal output froma wheel speed sensor provided in each of four wheels is taken out via aspecial signal line, to be then captured as a pulse of a wheel speedsignal through a binarization circuit, as illustrated in FIG. 5, or thata signal is directly captured from another calculator having a wheelspeed signal captured therein, for example, an ABS calculator via amemory, and an alarm is issued upon detection of a decrease in tireair-pressure, as illustrated in FIG. 6.

[0003] However, the alarming apparatus, in which the signal line is usedexclusively for each of the wheel speed signals, needs four pieces (orsets) of signal lines, and therefore, has been not acceptable in thecurrent circumstance in which the cost is to be cut down by reducing thenumber of lines as possible.

[0004] Furthermore, the above-described alarming apparatus, in which thewheel speed signal is captured from the other calculator via the memory,need to use both of the calculator and the memory. Consequently, thealarming apparatus must be mounted on a substrate on which thecalculator capturing the wheel speed signal is mounted, thereby arisinga problem of severe limitation of the freedom of design for mounting thealarming apparatus and the calculator.

[0005] In the meantime, there has been known an apparatus for detectinga decrease in tire air-pressure wherein a detection signal output fromthe wheel speed sensor is once captured into an ABS microcomputer as thewheel speed signal binarized in the binarization circuit, and then,captured information on the number of wheel speed pulses (i.e., data onthe number of pulses and a measurement time) is received via acommunication line (Japanese Unexamined Patent Publication No.71818/1998). The above-described detecting apparatus is simplified inconfiguration and reduced in cost by omitting an input interfacecircuit, which has been conventionally provided in a microcomputer fordetecting a decrease in tire air-pressure.

[0006] However, the communication line in the above-described detectingapparatus connects the ABS microcomputer to the microcomputer for anapparatus for alarming a decrease in tire air-pressure in a one-to-onecorrespondence, and therefore, the communication line is increased inlength in the case where the two microcomputers are positioned apartfrom each other, thereby arising problems of easy occurrence of acommunication error in addition to an increase in cost, resulting in thelow freedom of the layout of the microcomputer.

[0007] In view of the above-described circumstances, an object of thepresent invention is to provide an apparatus and a method for alarming adecrease in tire air-pressure, in which the cost of manufacturing can bereduced by using an on-vehicle communication network (hereinafterreferred to as an on-vehicle LAN).

SUMMARY OF THE INVENTION

[0008] In accordance with the present invention, there is provided anapparatus for alarming a decrease in tire air-pressure which alarms thedecrease in inner pressure of the tire by using a judged valuecalculated based on wheel speed information obtained from tires fittedto a four-wheeled vehicle, comprising calculating means for calculatingthe judged value based on the wheel speed information on each of thetires, the calculating means being connected to one of on-vehicle LANs,via which the wheel speed information on each of the tires istransmitted wherein the calculates means captures the wheel speedinformation on each of the tires via one of the on-vehicle LANs.

[0009] In accordance with the present invention, there is also provideda method for alarming a decrease in tire air-pressure which alarms thedecrease in inner pressure of the tire by using a judged valuecalculated based on wheel speed information obtained from tires fittedto a four-wheeled vehicle, comprising the step of capturing the wheelspeed information on each of the tires into calculating means forcalculating the judged value based on the wheel speed information oneach of the tires via one of on-vehicle LANs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a block diagram illustrating an embodiment of anapparatus for alarming a decrease in tire air-pressure according to thepresent invention;

[0011]FIG. 2 illustrates the state in which wheel speed information iscaptured in a first embodiment according to the present invention;

[0012]FIG. 3 is a block diagram illustrating the electric configurationof the apparatus for alarming a decrease in tire air-pressure of FIG. 1;

[0013]FIG. 4 illustrates the state in which wheel speed information iscaptured in a third embodiment according to the present invention;

[0014]FIG. 5 illustrates the state in which wheel speed information iscaptured in the prior art; and

[0015]FIG. 6 illustrates another state in which wheel speed informationis captured in the prior art.

DETAILED DESCRIPTION Embodiment 1

[0016] An apparatus and a method for alarming a decrease in tireair-pressure according to the present invention will be described belowwith reference to the accompanying drawings.

[0017] As shown in FIGS. 1 to 3, an apparatus for alarming decrease intire air-pressure according to Embodiment 1 of the present invention isso designed as to detect whether or not pneumatic pressures of fourtires FL, FR, RL and RR (W_(i), i=1˜4, 1: front left tire, 2: frontright tire, 3: rear left tire, 4: rear right tire) attached to, forexample, a four-wheeled vehicle are decreased, and is provided withpopular wheel speed information detecting means 1 respectively providedin connection with each tire W_(i).

[0018] The wheel speed information detecting means 1 takes the form of,for example, a wheel speed sensor for measuring a wheel speed from thenumber of rotation pulses generated by using an electromagnetic pickupof the like, or an angular velocity sensor for measuring a wheel speedfrom a voltage generated by using rotation by a dynamo electric.

[0019] An apparatus for alarming a decrease in tire air-pressure, whichis mounted on a vehicle, in the present embodiment is not speciallylimited as long as the apparatus is adapted to alarm a decrease in innerpressure of a tire by using a judged value calculated based on wheelspeed information obtained from tires fitted to a four-wheeled vehicle.The apparatus comprises, for example, wheel speed information detectingmeans for detecting wheel speed information on each of the tires, memorymeans for storing therein the wheel speed information on each of thetires, and calculating means for calculating a judged value based on thewheel speed information on each of the tires.

[0020] In the present embodiment, the wheel speed information (a wheelspeed signal) detected by wheel speed information detecting means 1disposed in each of the tires is captured into a calculator 2 for an ABSor the like, and then, the wheel speed signal is converted into digitaldata, so that data on the wheel speed information (i.e., wheel speeddata) is transmitted to an apparatus 4 for alarming a decrease in tireair-pressure via an on-vehicle LAN 3, and finally, is captured into theabove-described calculating means.

[0021] A rotational angular velocity of each of the tires is obtainedbased on the data on the wheel speed information. The sum of therotational angular velocities of a diagonal pair of tires is subtractedfrom the sum of the rotational angular velocities of another diagonalpair of tires. In the case where a ratio (a judged value) of thesubtraction result to an average value of the two sums exceeds apredetermined threshold value, a decrease in tire air-pressure isjudged, so that an alarm is issued.

[0022] To the apparatus 4 for alarming the decrease in tire air-pressureare connected a display 5 consisting of a liquid crystal displayelement, a plasma display element or a CRT for teaching a tire W_(i)having a decreased air pressure and an initialization switch 6 which canbe operated by a driver.

[0023] To the above-described on-vehicle LAN 3 are connected the ABScalculator, the apparatus for alarming the decrease in tire air-pressureand other calculators, for transmitting or receiving various data inaddition to the wheel speed data. A signal of the initialization switchor an alarm output for the display might be transmitted or received withthe use of the on-vehicle LAN 3.

[0024] As illustrated in FIG. 3, in the alarming apparatus 4, thecalculating means and the memory means are included in a calculatorconsisting of an I/O interface 4 a required for transmitting orreceiving a signal to or from the on-vehicle LAN 3, a CPU 4 b whichfunctions as a center of calculation, a ROM 4 c storing therein acontrol program for the CPU 4 b, and a RAM 4 d, in or from which data istemporarily written or the written data is read when the CPU 4 bperforms a control operation.

[0025] In the present embodiment, the wheel speed signal is convertedinto the digital data, which is then captured via the on-vehicle LAN,thereby remarkably reducing the number of the conventional signal lines.Consequently, the cost of manufacturing can be reduced. Moreover, theapparatus for alarming the decrease in tire air-pressure can be disposedwherever the on-vehicle LAN is laid, thus increasing the freedom ofdesign.

Embodiment 2

[0026] Next, a description will be given of another embodiment. Thewheel speed is very slightly varied according to the decrease in tireair-pressure. For example, the wheel speed is varied by about 0.2% withrespect to a decrease in pressure of 30%.

[0027] It is, accordingly, necessary to capture wheel speed informationwith high accuracy in order to detect the decrease in tire air-pressurein a short time with high accuracy. In view of this, 2 bytes (16 bits)are required as data on the wheel speed information per wheel, asillustrated below in Table 1. TABLE 1 WHEEL WHEEL WHEEL WHEEL SPEEDSPEED SPEED SPEED INFORMA- INFORMA- INFORMA- INFORMA- TION TION TIONTION OF WHEEL 1 OF WHEEL 2 OF WHEEL 3 OF WHEEL 4 (2 BYTES) (2 BYTES) (2BYTES) (2 BYTES)

[0028] Four times the data of 2 bytes per wheel, i.e., 8 bytes in total,are captured via one transmission, so that the data on the wheel speedinformation can be accurately captured with high efficiency.

Embodiment 3

[0029] As described by way of the above Embodiment 2, the wheel speedinformation can be captured in 2 bytes in the case where the receivabledata on the wheel speed information has been already calculated withsufficient accuracy. However, in the case where a wheel speed cannot becalculated since a high load is imposed on a microcomputer forcalculating wheel speed information, data on the wheel speed informationcannot be calculated, and therefore, the wheel speed information cannotbe captured in 2 bytes.

[0030] In this case, there is used wheel speed information that isexpressed by the combination of the number of pulses output inproportion to the rotation of a wheel (wheel speed pulses) and a timecorresponding to the number of pulses. For example, transmission orreception can be performed in the form of data on the wheel speedinformation illustrated in FIG. 4. In FIG. 4, each of points A and Bindicates a timing when the data on the wheel speed information isreceived. An interval of data received at the timing B is equivalent toa period of time T_(B) from the rising-up of a pulse immediately beforethe point A till the rising-up of a pulse immediately before the pointB. The number of wheel speed pulses during that period is indicated byN_(B). In a similar manner, an interval of data received at the timing Ais equivalent to a period of time T_(A), in which the number of wheelspeed pulses is indicated by N_(A). Here, each of the numbers N_(A) andN_(B) of wheel speed pulses is 1-byte data, and each of thecorresponding times T_(A) and T_(B) is 2-bytes data.

[0031] It is preferable that the interval for capturing the data on thewheel speed information ranges from 10 ms to 100 ms. This is because itis preferable that the data is captured at an interval within this rangein order to prevent any erroneous notice on an easy-to-slip road.

[0032] Incidentally, although the description has been given by way ofthe interval from the rising-up of one pulse to the rising-up of theother pulse in the present embodiment, the data might be captured at aninterval from the rising-down of one pulse to the rising-down of theother pulse.

[0033] As described above, according to the present invention, the wheelspeed information is converted into the digital data, which is thencaptured into the apparatus for alarming the decrease in tireair-pressure via the on-vehicle LAN, thus remarkably reducing the numberof lines laid in the vehicle in comparison with the prior art.Furthermore, the apparatus for alarming the decrease in tireair-pressure can be mounted wherever it can be connected to theon-vehicle LAN, thus enhancing the freedom of design of an electricalsystem inside the vehicle to allow the apparatus be mounted in arelatively great space.

What is claimed is:
 1. An apparatus for alarming a decrease in tireair-pressure which alarms the decrease in inner pressure of the tire byusing a judged value calculated based on wheel speed informationobtained from tires fitted to a four-wheeled vehicle, comprisingcalculating means for calculating the judged value based on the wheelspeed information on each of the tires, the calculating means beingconnected to one of on-vehicle LANs, via which the wheel speedinformation on each of the tires is transmitted wherein the calculatesmeans captures the wheel speed information on each of the tires via oneof the on-vehicle LANs.
 2. The apparatus of claim 1, wherein the wheelspeed information per wheel is 2 bytes, and wheel speed information forfour wheels is captured via one transmission.
 3. The apparatus of claim1, wherein the wheel speed information is one expressed by a combinationof the number of pulses output in proportion to rotation of a wheel anda time corresponding to the number of pulses, and the number of pulsesand the corresponding time are received in 1 byte and 2 bytesrespectively.
 4. The apparatus of any one of claims 1 to 3, wherein aninterval for capturing the data on the wheel speed information rangesfrom 10 ms to 100 ms.
 5. A method for alarming a decrease in tireair-pressure which alarms the decrease in inner pressure of the tire byusing a judged value calculated based on wheel speed informationobtained from tires fitted to a four-wheeled vehicle, comprising thestep of capturing the wheel speed information on each of the tires intocalculating means for calculating the judged value based on the wheelspeed information on each of the tires via one of on-vehicle LANs. 6.The method of claim 5, wherein the wheel speed information per wheel is2 bytes, and wheel speed information for four wheels is captured via onetransmission.
 7. The method of claim 5, wherein the wheel speedinformation is one expressed by a combination of the number of pulsesoutput in proportion to rotation of a wheel and a time corresponding tothe number of pulses, and the number of pulses and the correspondingtime are received in 1 byte and 2 bytes respectively.
 8. The method ofany one of claims 5 to 7, wherein an interval for capturing the data onthe wheel speed information ranges from 10 ms to 100 ms.